Achereiner, Frédéric

Abstract [en]

This Master’s Thesis deals with the development of new polymer foams with very small cell size, the PolyHIPEs, and their applications. The area of application studied was papermaking. The porous polymers were used as filler material in paper sheets, with the purpose of increasing light scattering in light-weight paper grades, and thus their brightness and opacity. The work was divided in two parts: The first part concerns the development of the polymer foams themselves. Since this is a rather novel area, only few research teams in the world are currently working with these. So the development had to be started nearly from scratch. This implies starting with the preparation of a High Internal Phase Emulsion (HIPE) with 90% of water and a styrene-based oil phase. This was done by using the Phase-Inversion Temperature method. The composition of the system and all the other parameters were tailored to obtain the smallest droplet size possible. Then the oil phase of the HIPE was polymerised, to form the PolyHIPE. After washing and drying, this gave a dry monolith of highly porous polymer. The internal structure, observed by Scanning Electron Microscopy, was very specific to PolyHIPE: polyhedral cells interconnected through holes in the cells walls. The cell size was in the range of 1 to 2 µm and the connecting holes were mainly between 0.1 and 0.6 µm in diameter. The second part deals with the application of PolyHIPEs to papermaking. To be used in paper, the new polymer foam had first to be reduced into a powder, while keeping intact the specific internal structure. This was done by crushing it in ethanol using an Ultraturrax apparatus. Then test were done to determine the quantity of filler retained in the paper. The results indicated that only 40 to 50% of the filler was mechanically trapped in the paper. Retention agents were of no real use. Finally, paper sheets containing filler were prepared. Observation with Scanning Electron Microscopy confirmed that the filler was retained in the paper. Reflectance measurements indicated a positive effect on brightness and opacity. More experiments have to be done to determine exactly the effects of PolyHIPEs in paper, but these new polymer foams have definitely a future in this area.